1. Field of the Invention
The present invention relates in general to a head-up display using hologram optical devices for automobiles and, more particularly, to a head-up display using a light transmission hologram optical device as well as a light reflection hologram optical device for displaying automobile conditions, such as traveling velocity, rpm, fuel quantity and engine temperature, and a warning signal of opened window, on a holographic combiner mounted to a windshield of the automobile, and for displaying the conditions of dead ground of a large truck or of a special freight car, such as a container car or a ready mixed concrete car.
2. Description of the Prior Art
With reference to FIGS. 1 and 2, there are shown a typical head-up display for an automobile and a typical holographic combiner of the head-up display disclosed in U.S. Pat. No. 4,613,200 respectively. Typically, such a head-up display is only installed in an expensive automobile due to the high cost of the display. In FIG. 1, the reference numeral 10 denotes an optical projection system which is installed in an engine chamber of the automobile. In the optical projection system 10, automobile conditions, such as traveling velocity, rpm, fuel quantity and engine temperature, are converted into electric signals. The signals in turn are converted into image information by a cathode ray tube (CRT) 11 of the optical projection system 10. The image information from the CRT 11 is magnified by an optical lens system 12 and, thereafter, projected on the holographic combiner 20 by means of a reflection mirror 13, so that the combiner 20 displays thereon the automobile conditions in the form of an image. Here, the automobile conditions displayed on the holographic combiner 20 come into the view of a driver 50, so that the above head-up display informs the driver 50 of the automobile conditions.
The above head-up display lets a driver observe various automobile conditions displayed on the combiner 20 mounted to the windshield while watching carefully the forward area (front) of the traveling automobile. Thus, the head-up display not only provides considerable convenience for the driver in operating the automobile, but also prevents possible traffic accidents which may be suddenly generated when the driver temporarily turns down the eyes in order to observe the typical dashboard, which typical dashboard is placed about a steering wheel.
However, the above head-up device has a problem that both the optical projection system and the holographic combiner have complicated constructions and the displayed image on the combiner is often overlapped.
In an effort to overcome the above problem of the head-up display, a holographic combiner which is produced by forming multiple coating layers on a sheet of glass is used. However, this holographic combiner increases the cost of the head-up display due to the multiple coating layers formed on the glass sheet.
In addition, there has been proposed a holographic combiner produced by bonding a hologram optical device to two sheets of glass as shown in FIG. 2. In this case, the hologram optical device 20' is interposed between two sheets of safety glass 1 and bonded to the two sheets of safety glass 1 by means of adhesive 4 (not shown). However, the process for producing this holographic combiner is very complicated and difficult.
Meanwhile, it is noted that careful watching of the forward area of a traveling automobile is more important than observing the dashboard during operation of the automobile.
Particularly when backing up a conventional large truck or a conventional special freight car, such as a container car or a ready mixed concrete car, the driver must back the car based on his experience, viewing the images of the opposed rear side area conditions reflected in the opposed rear mirrors and the image of the backward area conditions reflected in the room mirror.
Furthermore, when the truck or the special freight car is loaded with freight in its freight compartment, the backward (rear) area conditions cannot be reflected in the room mirror due to the freight loaded in the freight compartment, thus to form dead ground in the backward area of the car. In this case, the driver must back the car based on the images of the opposed rear side area conditions reflected in the opposed rear mirrors, while leaving the conditions of the dead ground of the backward area of the car to his conjecture.
In view of intrinsic use of the large truck, it is frequently required to precisely drive the truck to a desired freight unloading place. In the case of a container car which is a kind of special freight car, it is required to precisely drive a tractor to a trailer for coupling the tractor to the trailer without failure. In the case of a ready mixed concrete car, which is a kind of special freight car, it is required to drive the car in order to precisely align the concrete discharge port of the car to a desired concrete pouring position. In this regard, the driver often drives the large truck or the special freight car based on his skill or with help from other people.
The large truck or the special freight car typically has a larger dead ground in its backward area due to its large size, so that the large truck or the special freight car is proved to be a dangerous car, particularly, to a careless pedestrian such as infant.
Therefore, in order to prevent possible traffic accidents due to the dead ground of the backward area of a large truck or of a special freight car, the driver of the car needs to be informed of conditions of the backward area of the car when driving and, more particularly, backing up the car.